1. Field of the Invention
The present invention relates generally to an electrical control system for use in computer control, and more particularly to a control system such as an engine control system with one or more microcomputers and an associated hardware circuit having electrically reconfigurable logic when power is applied.
2. Description of Related Art
In recent years there have been several improvements in electrotonic control systems for automobile engines, particularly computer-controlled internal combustion engines adaptable for use in various types of automotive vehicles. One significant concept for improving reliability is to employ a backup circuit in addition to a microcomputer for fuel-injection control of an associated engine. The backup circuit may be a digital hardware (hard-wired) circuit that is relatively simple in circuit configuration, and is adapted for providing backup operations to replace the microcomputer which may fail in operation, thereby ensuring that an automobile continues running with enhanced safety even during malfunction of the microcomputer.
Typically, the microcomputer for engine control is operative with an operation guarantee voltage of about 4 volts. This means that the microcomputer reliably operates only when its operating voltage is above 4 volts. If a battery is degraded in performance, it may possibly happen that a power supply voltage to the microcomputer becomes intermittently lower than the operation guarantee voltage when its electrical load increases for starting an engine. If this is the case, the "backup" hardware circuit offers its importance: this circuit is rendered operative providing backup operations to retain normal operations without assistance of the malfunctioning microcomputer.
This engine control system, however, suffers from a problem in that the backup circuit is required to change in hardware configuration every time for each type of automobile with different engine specifications. This necessitates that different backup circuits should be designed and produced for different applications. One possible approach to avoid such redundant design and production of backup circuits is that the backup circuit is designed to be changeable or "reconfigurable" in internal logic circuitry by physically changing or rearranging a pattern of aluminum lead-wire connections of a large scale integrated circuit (LSI) incorporating preinstalled circuit elements that make up a specific circuit configuration as selected. However, this does not come without accompanying disadvantages: an increased number of mask patterns should be manufactured which corresponds to the number of possible different circuit configurations under modification, which requires troublesome and time-consuming work.
To avoid the problem, the inventors considered an improved reconfigurable backup circuit, which is developed using the microcomputer technology as disclosed, for example, in Published Unexamined Japanese Patent Application (JP-A) 2-159613. With the circuit, a built-in read only memory (ROM) of an engine control microcomputer stores data for use in setting the backup circuit into a desired internal logic configuration. By accessing the ROM to read the circuit configuration set data to reconfigure the backup circuit to meet a present need, it becomes possible to make the hardware arrangements of the backup circuit per se common or uniform among a wide variety of applications.
One drawback to this approach, however, is that system malfunction may still possibly occur due to unavailability of the backup circuit during a certain period ranging from the end of reset-release to the actual completion of reconfiguration of the backup circuit. More specifically, reading of the configuration set data pre-stored in the ROM is kept unattainable until when reset-releasing of a central-processing unit (CPU) of the microcomputer is completed after power is applied, namely power-on. If the microcomputer starts performing its inherent control operations immediately after the completion of such reset-release, the microcomputer is forced during the period into an undesirable condition where it must execute control operations while the backup circuit is in the process of being reconfigured. This may result in an increase in the possibility of the occurrence of system malfunction as a whole.